Chromosome rearrangement between the Indian muntjac and Chinese muntjac is accompanied by a delection of middle repetitive DNA.

The organizations of the genomes of two related species of Asian deer, the Indian (2n = 6 female, 7 male) and Chinese muntjac (2n = 46), were compared at the cytogenetic and molecular levels. These dramatically different karyotypes preserve little apparent G-banding homology. The difference in chromosome number is coincident with a 22% reduction in haploid DNA content from 2.7 to 2.1 pg in the Chinese and Indian muntjac, respectively. The kinetics of reassociation of the Indian muntjac (equivalent Cot = 4285 M-1. s-1) and Chinese muntjac DNA (equivalent Cot - 4362 M-1.s-1) in 2.4 M tetraethylammonium chloride suggests conservation in amount of "single-copy" DNA. Two middle repetitive DNA sequence classes differ in both amount and in degree of repetition between the two species. A middle repetitive frequency component (935-fold repeated) represents 13% of the Indian muntjac DNA. A similar component (644-fold repeated) represents 17% of the Chinese muntjac DNA. Low repetition DNA sequence components (repeated 5- and 50-fold) represent 30 and 40% of the Indian and Chinese muntjac DNAs, respectively. These differences quantitatively account for the 0.6 pg haploid DNA content variation between species. The deletion of middle repetitive DNA has not substantively altered the distribution of restriction endonuclease DNA base composition classes as defined by buoyant density in cesium chloride. These results represent the first time that middle repetitive DNA has been directly implicated in a chromosome rearrangement within the vertebrates.

Interaction of anthracyclines with DNA and chromosomes.

Daunomycin and adriamycin were previously found to produce Q-like banding patterns on chromosomes. The interaction of several anthracyclines with both natural and synthetic DNAs and chromosomes has been investigated in more detail. Daunomycin fluorescence is almost completely quenched by natural DNAs with varying base composition from 31 to 72% G-C and by the alternating polymer poly-d(G-C).poly-d(G-C). In contrast, daunomycin fluorescence is quenched by only 50% when the dye interacts with synthetic A-T polymers. Thus, differential quenching of daunomycin fluorescence can account for the production of bright bands at contiguous A-T sequences along the chromosome. Slight differences in fluorescence quenching between the repeating and homopolymeric A-T duplex DNAs were observed which can be attributed to differences in affinity of daunomycin for these DNAs. The aminosugar moiety of daunomycin, daunosamine, increases the binding of daunomycin to DNA and also enhances chromosome banding.--Nogalamycin, which displays no differential quenching with the different DNAs in solution, also fails to produce bands on chromosomes.--These findings suggest that non-random nucleotide sequence arrangements along the chromosome are a basic determinant for dye interaction to produce the observed banding patterns. Specific banding procedures may determine the accessibility of these sites within the chromosomal DNA.